Chronic arterial insufficiency of the upper extremity is much less common than that of the lower extremity. The Allen test, which determines the patency of the radial and ulnar arteries, can be used to assess whether arterial insufficiency exists in the upper extremity. (The ulnar artery is normally not palpable.) This test takes advantage of the radial-ulnar loop. The examiner first occludes the radial artery by applying firm pressure over it. The patient is asked to clench the fist tightly. The patient is then asked to open the fist, and the color of the palm is observed. The test is repeated with occlusion of the ulnar artery. Pallor of the palm during compression of one artery indicates occlusion of the other.
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